The present invention relates to a process for the production of combustion-modified foams and to the foams produced by that process.
Foams based on aromatic isocyanates are known to be flammable if they have not been treated in some manner to increase their fire resistance.
Side effects of combustion such as the optical smoke density (hereinafter called simply smoke density) may be more of a hazard in the event of fire than the fire itself. The smoke density is therefore becoming increasingly important in the discussions about the risks during fires involving isocyanate-based foams.
Attempts to protect foams based on aromatic isocyanates against ignition by the addition of metal compounds (such as antimony trioxide) have been made. Heavy metal oxides such as antimony trioxide can reduce the smoke density but often give rise to the risk of an increased heavy metal load.
The use of Mg(OH).sub.2 has already been proposed for various plastics materials, for example polyethylene and polypropylene (see, for example, in Plastics Technology, July 1985, page 70 et seq), and for polyurethanes based on hexamethylene diisocyanates (JA 58-225,116, Hitachi Cable), but not for foams based on aromatic isocyanates.
The use of Mg(OH).sub.2 as an ancillary agent in certain flame- or smoke-suppressing combinations has been disclosed for use with polyurethanes. E.g., U.S. Pat. No. 3,737,400 and British Patent No. 1,527,668. U.S. Pat. No. 3,737,400 discloses flame-suppressing mixtures for polyurethanes that may optionally contain Mg(OH).sub.2 and certain other inorganic compounds, but which must always contain at least one of ammonium sulfate or aluminum hydroxide hydrate. This reference states that the optional compounds, including Mg(OH).sub.2, would be ineffective if used alone. British Patent No. 1,527,668 similarly teaches inter alia the use of a mixture of Mg(OH).sub.2 and alumina trihydrate as a flame- or smoke-suppressing agent for polyurethanes.
Flame-proofing compositions which at least theoretically contain Mg(OH).sub.2 in combination with other substances have been disclosed for use with polyurethanes. U.S. Pat. No. 3,951,885 discloses magnesium oxychloride cement, a reaction product of magnesium chloride and magnesium oxide which is believed to be a complex containing or derived from Mg(OH).sub.2, MgCl.sub.2, and water. See also U.S. Pat. Nos. 3,778,304 and 3,963,849.
The above-mentioned references do not teach the use of Mg(OH).sub.2 in the absence of inorganic compounds as a smoke-suppressing agent for polyurethanes exposed to fire.